This invention relates to thermal storage units (TSUs). More particularly, this invention relates to TSUs that provide sensible heat thermal energy storage and delivery in a way that increases efficiency and reduces costs compared to known TSUs.
TSUs are well known and are often used in power delivery systems, such as compressed air storage (CAS) systems and thermal and compressed air storage (TACAS) systems. Such systems, often used to provide an available source of electrical power, often use compressed air to drive a turbine which powers an electrical generator.
In TACAS systems, it is desirable to heat the compressed air prior to reaching the inlet port of the turbine. It is known that heated air, as opposed to ambient or cool air, enables the turbine to operate more efficiently. Therefore, a mechanism or system is needed to heat the air before providing it to the turbine. One approach is to use a suitable type of fuel-combustion system. Another approach is to use a TSU. While fuel-combustion systems usually emit polluting gases, TSUs may be preferable over fuel-combustion systems at least because they are not associated with such harmful emissions.
Although TSUs may offer advantages over fuel-combustion systems, existing TSUs have several shortcomings, as discussed below. Moreover, TSUs are typically designed to take many of the following design considerations into account:
(1) the physical dimension of the TSU;
(2) the TSU's capacity to heat fluid to a predetermined temperature;
(3) the thermal energy storage capacity of the TSU;
(4) the mass flow rate of fluid flowing through the TSU;
(5) the ability to minimize the pressure drop of fluid as it flows through the TSU;
(6) the ability to heat the fluid using forced convection heating;
(7) providing reliable and safe operation in high pressure applications; and
(8) low manufacturing costs.
Conventional TSUs, such as those shown in FIGS. 1 and 2, may not be able to accommodate many or all of the forgoing criteria.
TSU 10 of FIG. 1 includes heated parallel plates 12 contained within housing 14 to create channels through which compressed gas may flow. The heat transfer area and the gap between plates 12 may be adjusted for optimum heat transfer conditions. Such a TSU, however, is not optimally suited for high pressure operation as these plates do not provide optimum pressure containment for the compressed gas, and instead result in leakage flow between plates 12 and housing 14.
Another known TSU uses tube flow through elongated cavities embedded in a solid medium. As shown in FIG. 2, compressed gas travels through through-holes 22, which are bored out of bar 24. Although tube flow, as provided by TSU 20 of FIG. 2, may provide more desirable pressure containment compared to channel flow TSU 10 of FIG. 1, it involves high fabrication costs. This is because it is usually costly to drill a plurality of small-diameter holes that extend throughout the entire length of a solid medium.
Therefore, it can be seen that the TSUs shown in FIGS. 1 and 2 fail to provide means for effectively containing and delivering heated and compressed air in a manner that is cost beneficial. In addition, it can be seen that the foregoing TSUs are limited in design flexibility at least because they either require machining or assembly of several parts to provide fluid conducting passageways.
In view of the foregoing, it is an object of this invention to provide a low-cost TSU that provides efficient heat storage, heat delivery and pressure containment.
It is also an object of the invention to provide enhanced design flexibility to better adhere to predetermined design criteria.